1. Field of the Invention
The present invention relates to a packaging box which is mainly used for packaging frozen food with an improved heat-insulating property. Also, the article according to the present invention may be used for packaging material to keep the content therein warm.
2. Description of the Prior Art
Conventionally, a box that is injection-molded of foamed polystyrene resin is used in a field in which a high heat-insulating property is needed. This box is superior in heat-insulating property but needs an individual molding die in accordance with the shape and dimension of the box. This is costly. Also, it is impossible to apply the technique to the article except for mass production. Also, since the polystyrene resin box has a large thickness and is not collapsible, there is a problem in that the spaces necessary for transportation, storage and maintenance are large. In addition, there is the situation where the lower boxes of the stacked boxes would be damaged or deformed due to their low mechanical strength.
On the other hand, a conventional corrugated card-board box is in the form of a sheet and may be transported with ease. Although corrugated card-board box needs a small space, they are insufficient in terms of heat-insulating property.
In order to overcome the above-noted defects inherent in the prior art, it is an object of the present invention to provide a heat-insulation packaging box whose required space is small, which is easy to adapt to change in configuration and dimension, which is easy to stack in sheets for transportation, storage and maintenance, which is easy to assemble for use, and which is superior in heat-insulating property to the conventional corrugated card-board box.